Carrots Share Trait With Tiny Pea Aphid

There’s a reason your parents kept after you to eat your carrots. The vegetables (and lots of others, too) supply carotenoids, compounds that are good for vision and overall health. Animals, humans included, cannot manufacture them.

Check that. Researchers have found the first evidence of carotenoid production in a member of the animal kingdom. The animal in question? A tiny aphid.

Photo

Pea aphids are the first creatures in the animal kingdom to have been shown to produce carotenoids.Credit
Charles Hedgcock, R.B.P

Nancy A. Moran, a researcher at the University of Arizona who is soon to be at Yale, and Tyler Jarvik, an Arizona colleague, report in Science that the pea aphid, Acyrthosiphon pisum, produces carotenoids using a genetic sequence that it picked up from fungi as it evolved, a process called lateral gene transfer. The carotenoid production contributes to an unusual characteristic of pea aphids: they come in two colors, red and green.

Dr. Moran, who studies genomic evolution, made the discovery while searching through the pea aphid genome, which was sequenced last year. The genes for carotenoid production are similar for every organism that makes them, she said, and they just “popped up” when she did the search. Further analysis showed that they came from fungi, and that the transfer occurred tens of millions of years ago.

All pea aphids have this carotenoid-making machinery, but the researchers found that some have a genetic mutation and cannot produce certain carotenoids that are red in color. So these aphids are green, while those without the mutation are red.

This division in color has an ecological effect: red aphids are more likely to be eaten by predators, while green ones are more likely to be invaded by parasites. In turn, this split between predation and parasitism helps maintain the split in color, ensuring that neither red nor green prevails over the long term.

Correction: May 4, 2010

An earlier version of this article misstated the affiliation of Nancy A. Moran. The article also misstated the ecological effect the division in color has on the aphids.

A version of this article appears in print on May 4, 2010, on page D3 of the New York edition with the headline: Carrots Share Trait With Tiny Pea Aphid. Order Reprints|Today's Paper|Subscribe